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Date: Mon, 5 Aug 2013 18:50:34 +0200 From: Oleg Nesterov <oleg@...hat.com> To: Ingo Molnar <mingo@...nel.org> Cc: Steven Rostedt <rostedt@...dmis.org>, Frederic Weisbecker <fweisbec@...il.com>, Peter Zijlstra <peterz@...radead.org>, David Ahern <dsahern@...il.com>, Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>, "zhangwei(Jovi)" <jovi.zhangwei@...wei.com>, linux-kernel@...r.kernel.org Subject: [PATCH 0/3] Teach perf_trace_##call() to check hlist_empty(perf_events) Sorry for double post, forgot to cc lkml... On 07/19, Ingo Molnar wrote: > > * Oleg Nesterov <oleg@...hat.com> wrote: > > > Hello. > > > > The patches are the same, I only tried to update the changelogs a bit. > > I am also quoting my old email below, to explain what this hack tries > > to do. > > > > Say, "perf record -e sched:sched_switch -p1". > > > > Every task except /sbin/init will do perf_trace_sched_switch() and > > perf_trace_buf_prepare() + perf_trace_buf_submit for no reason(), > > it doesn't have a counter. > > > > So it makes sense to add the fast-path check at the start of > > perf_trace_##call(), > > > > if (hlist_empty(event_call->perf_events)) > > return; > > > > The problem is, we should not do this if __task != NULL (iow, if > > DECLARE_EVENT_CLASS() uses __perf_task()), perf_tp_event() has the > > additional code for this case. > > > > So we should do > > > > if (!__task && hlist_empty(event_call->perf_events)) > > return; > > > > But __task is changed by "{ assign; }" block right before > > perf_trace_buf_submit(). Too late for the fast-path check, > > we already called perf_trace_buf_prepare/fetch_regs. > > > > So. After 2/3 __perf_task() (and __perf_count/addr) is called > > when ftrace_get_offsets_##call(args) evaluates the arguments, > > and we can check !__task && hlist_empty() right after that. > > > > Oleg. > > Nice improvement. > > Peter, Steve, any objections? Ingo, It seems that everybody agree with this hack but it was forgotten, let me resend it again. The only change is that I added the following tags: Tested-by: David Ahern <dsahern@...il.com> Reviewed-and-Acked-by: Steven Rostedt <rostedt@...dmis.org> Oleg. include/trace/events/sched.h | 22 ++++++++-------------- include/trace/ftrace.h | 33 ++++++++++++++++++++------------- 2 files changed, 28 insertions(+), 27 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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